1. Field of the Invention
The present invention relates to a method of and an apparatus for controlling a continuously variable valve timing mechanism of an internal combustion engine, to continuously and variably control the open/close timing of an intake or exhaust valve of the engine according to a target timing.
2. Description of the Related Art
There are many variable mechanisms that optimize the open/close timing of a valve of an automobile engine according to driving conditions. One of them is an ON/OFF mechanism, which changes the timing of an intake valve of the engine from normal timing to early timing when an engine load exceeds a switching threshold. Japanese Unexamined Utility Model Publication No. 3-99844 decreases the switching threshold or increases a detected engine load in response to a decrease in atmospheric pressure, to optimize the valve timing.
To provide high-performance engines, continuously variable valve timing mechanisms for optimizing valve timing at all times have been developed in place of the ON/OFF mechanisms, as disclosed in Japanese Unexamined Patent Publication No. 4-175430 (corresponding to U.S. Pat. No. 5,271,360). This mechanism continuously changes the open/close timing of a valve, and therefore, never employs the idea of changing the switching threshold in response to a change in atmospheric pressure. There is a requirement, therefore, to provide a method of properly controlling the continuously variable valve timing mechanism.